What is known as a virtual camera refers to sets comprising a real recording camera and a habitually electronic image data processing device, which produce an output signal with a coded image or a coded image sequence, wherein the perspective of the coded images does not match the perspective of the recording camera. On account of the loss of information when a real three-dimensional object is mapped into a two-dimensional image data model by a real recording camera, the virtual camera is able to reproduce non-moving objects correctly particularly when they are approximately flat.
Virtual cameras have been proposed as driver assistance devices in motor vehicles. These are particularly what are known as top view systems or omnidirectional cameras. These typically comprise a plurality of real recording cameras which are arranged in or on a vehicle and which are used to produce a chronological sequence of image data records. The image data in the image data records are subjected to different transformations in a typically electronic image data processing device and are mixed to form a chronological sequence of overall image data. This makes it possible to obtain, by way of example, a view of the surroundings of the vehicle from a perspective above the vehicle roof. This chronological sequence of overall image data can be continuously displayed to the driver of the motor vehicle on a display apparatus in order to simplify shunt or parking manoeuvres.
It is evident that in a virtual camera with a plurality of real recording cameras the quality of the overall image delivered is distinctly dependent on the exact knowledge of the positions and directions of the real recording cameras. The more accurately that these data are known, the easier that it is possible to determine the transformation that determines the best possible image quality in the area of adjacent recording areas. Against this background, there have been a series of proposals involving either the automatic determination of the positions and directions of the recording cameras or the correction of errors in these variables in relation to initially stored values.
An omnidirectional camera with automatic calibration is revealed by the officially published document DE 10 2007 043 905 A1. Said document proposes identifying an object element in the image data for the purpose of the calibration. The recognition of mapped areas of the outer vehicle skin is recognized as particularly advantageous. The proposed approach is intended to allow compensation for, inter alia, situational changes in the real recording cameras on the vehicle on account of vibrations, ageing and thermal or mechanical stresses.
However, the known method is based on the processing of information from a model of the real world and particularly on the processing of information regarding the shape of the outer vehicle skin.